The present invention relates to a plasma arc torch or heat source, and more particularly to the anode of the torch.
In the metals and ceramic processing industries, high temperatures are needed for various tasks and processes such as continuous casting, sintering and welding. One method of producing the high temperatures required for these processes is through the use of a plasma arc torch.
The plasma arc torch operates by creating an intense electromagnetic field which ionizes a gas medium to form a discharge, or thermal plasma. An electric arc is struck between a pair of electrodes to heat a working gas. The gas extends the arc and it is heated by the arc such that it becomes ionized and disassociated to form the plasma. The thermal plasma may have an operating temperature range of from 2000.degree. to 11000.degree. K. Torches can operate in a so-called transferred mode, wherein the arc and plasma jet extend from a nozzle to the workpiece being heated, or in a so-called non-transferred mode, in which case the arc impinges the wall of the nozzle which functions as an anode and only the plasma effluent is projected as a jet beyond the nozzle toward the workpiece or wherever one wishes to direct the flow of plasma. The basic operation of torches of this type are described in U.S. Pat. No. 2,960,594. Another example of a plasma arc torch is disclosed in U.S. Pat. No. 4,570,048 to Poole, the teachings of which are incorporated herein by reference.
To control the operation of the torch, it is necessary to regulate both the flow of the gas medium through the torch and the supply of electric power to the torch. The geometry of the anode, which also serves as the nozzle through which the gas flows and the plasma arc extends, has been found in prior art devices to provide a further means of controlling the operation of the torch. If the nozzle allows the plasma arc to wander, unstable operation of the torch results, regardless of the regulation of the gas flow or the electric power supply.
Unstable operation of the plasma torch will complicate application of the torch to a workpiece and result in damage to the nozzle in the form of erosion of the electrodes. Erosion necessitates frequent replacement of the electrodes which reduces the time that the torch can be used and increases the time required for maintenance. Additionally, many devices of the prior art operate their torches efficiently only in a narrow range of gas flows and power supplies. The Poole design (U.S. Pat. No. 4,570,048) presented a torch that operated over a range of operating conditions, but required an anode design with a sharp knife edge transition.
Thus, there is a need for improvements in or alternatives to the existing plasma arc torches and anode designs which will allow for operations at high thermal efficiencies and different heating requirements.
Accordingly, it is an object of the present invention to provide a plasma torch having an improved anode design.
It is another object of the present invention to provide applasma torch that operates at a high thermal efficiency.